Proper design of a piston pin/connecting rod joint of reciprocating piston engines is critical to overall engine reliability and durability. Perhaps nowhere are the demands greater than heavy-duty diesel engines where heavy loads and long life are foremost on a long list of design requirements.
Insert bearings have been used in numerous bearing applications including, but not limited to, engine main and connecting rod bearings, railway vehicle axle bearings and engine piston pin bearings of various types. In the particular case of engine piston pin bearings, a commonly used application has been as the main load-carrying bearing in the oscillating piston pin joint of two-cycle engine pistons. Pertinent examples of the latter include U.S. Pat. No. 3,433,539 to Nigh, U.S. Pat. No. 3,555,972 to Hulsing and U.S. Pat. No. 3,762,389 to Malina.
In four-stroke cycle engine pistons, the operating conditions may impose significant reverse loads on the piston pins during the piston intake and exhaust strokes when outward centrifugal forces are not significantly counteracted and may be added to by low or below ambient cylinder pressures acting on the pistons. Thus, in four-stroke cycle piston assemblies, load carrying bearings are commonly required on both the top and bottom sides of the piston pin. Known constructions include the use of individual insert bearings as in U.S. Pat. No. 2,850,340 to Brill and U.S. Pat. No. 3,943,908 to Kubis et al. A one-piece insert bearing with extended upper surfaces is shown in U.S. Pat. No. 2,069,594 to Schneider and a three-piece insert bearing with an extended upper surface is shown in U.S. Pat. No. 4,644,853 to Russell et al. These arrangements provide load-carrying capabilities in both directions of piston reciprocation and a close pin-to-bearing clearance.
Development testing of a recent four-stroke diesel engine indicated that to attain long life with high loads special attention in the piston pin bearing area would be needed. Development focused on a one-piece, 360.degree. bearing that provided a full width bearing surface on the upper compression loaded side. In the lower inertia loaded side, the bearing was extended circumferentially from the upper side in the ear section of the piston head to form a complete 360.degree. bearing surface. As it was configured for production, the one-piece bearing was pressed in place and finish machined to a cylindrical shape as by boring and/or broaching. The negative impact of this design on producibility, serviceability and cost became apparent with time. Although without functional problems in the field, a development program was pursued to relieve these concerns. A number of conceptual designs were proposed that incorporated prefinished bearings that were installed and retained in different ways.